First off I would suggest you drive both of them. There is a world of difference in the cab between the E Series and Sprinter, how they drive and what it's like to be in in the cab on the road.
Also you need to know how much stuff you want to carry/tow. The Monaco will likely have a higher cargo capacity (known as OCCC) and should have a higher combined gross weight rating.
The Winnie will beat the Monaco in on fuel economy but has a smaller tank than most Fords so the Ford may have more range per tank. If you do your own periodic maintenance the Sprinter is pretty easy to work on....lots of room under the hood and good access. Fords, well not so much....small hood 10 lbs of engine in a 5 lb bag...
The Sprinter cab chassis costs more than a Ford so it shows up in the final price of the RV. Ford long ago amortized much of the cost of the E series...it's an old design (and it shows in many ways).
There is a new version of the Sprinter coming out next year so it will likely be showing up on 2015 (or so) RVs. It will have more magic safety stuff and tech wizardry than the current Sprinter (additions beyond stability control, like cross wind assist).